1. Field of the Invention
The present invention relates to a heat treatment apparatus for performing heat treatment of various substrates such as a semiconductor wafer, a ferrite substrate for magnetic recording and the like by heating means, and more particularly, it relates to a heat treatment apparatus which measures the temperature of a substrate under heating on the basis of output signals from thermocouple mounted on the substrate.
2. Description of the Prior Art
In a conventional heat treatment apparatus for thermally treating a substrate such as a semiconductor wafer by heating means, control data for driving the heating means, i.e., the so-called profile data, are previously stored in a memory. In order to thermally treat the treated substrate by such a heat treatment apparatus, the heating means is controlled by a computer on the basis of the profile data so that heat treatment is executed by a required temperature program for the treated substrate. In order to create the profile data in the heat treatment apparatus, a temperature measuring substrate is independently prepared by the same material with the treated substrate. A thermocouple is mounted on the temperature measuring substrate, which in turn is contained in a heating furnace and appropriately heated, to measure surface temperatures of the substrate from hour to hour on the basis of output signals from the thermocouple, thereby to obtain data required for creating the profile data.
In such a heat treatment apparatus, heat treatment of the treated substrate is generally executed by closing the door of the heating furnace to bring the furnace into an airtight state and maintaining the furnace under a vacuum or required gas atmosphere. In order to create profile data of high accuracy, therefore, it is also necessary in temperature measurement of the temperature measuring substrate contained in the heating furnace to bring the furnace into an airtight state, thereby to keep the furnace in the same condition as that for heat treatment of the treated substrate. However, when temperature measurement of the temperature measuring substrate as hereinabove described, it is necessary to extract two types of metal wires forming the thermocouple from the furnace to obtain output signals from the thermocouple. Such metal wires have generally been extracted from a clearance formed by slightly opening the door of the heating furnace, whereby air-tightness in the furnace is deteriorated and correct data cannot be obtained.
As a method of extracting the two types of metal wires forming the thermocouple from the furnace while securing air-tightness in the furnace, a wire hole may be provided in a furnace wall portion to pass the metal wires through the wire hole. In such a method, however, it is necessary to once draw out ends of the two types of metal wires, being previously passed in the furnace through the wire hole, from an inlet of the heating furnace to connect the same to the temperature measuring substrate and thereafter contain the metal wires again in the furnace with the temperature measuring substrate. Thus, the metal wires of the thermocouple may loosen when the temperature measuring substrate is introduced into the furnace, to be entangled with each other. Such entanglement of the metal wires may also take place when the temperature measuring substrate is extracted from the furnace. Probability of such entanglement of the metal wires is increased particularly when a plurality of thermocouples are mounted on the temperature measuring substrate in order to measure surface temperature distribution of the temperature measuring substrate.